1. Technical Field
The present invention relates to an oxidation treatment method and an oxidation treatment apparatus for an object to be treated, such as a semiconductor wafer.
2. Description of Related Art
The process of fabricating a semiconductor device, for example, includes an oxidation treatment step for forming an oxide film on the surfaces of a semiconductor wafer that is an object to be treated, and one method of performing such an oxidation treatment is a method of oxidizing a semiconductor wafer by bringing it into contact with water steam at a predetermined temperature within a treatment furnace (wet oxidation). To perform this oxidation treatment, an oxidation treatment apparatus is known in which a combustion device which causes hydrogen and oxygen to react (combust) and generate water steam is provided independently outside the treatment furnace, and the water steam generated by this combustion chamber is supplied into the treatment furnace to perform the oxidation treatment, as disclosed in Japanese Patent Application Laid-Open No. 63-210501, for example.
In the prior-art oxidation treatment apparatus, the treatment is preformed with the interior of the treatment furnace being controlled to a very slightly reduced pressure, such as approximately -5 mm H.sub.2 O to -10 mm H.sub.2 O with respect to atmospheric pressure (760 Torr) by a factory exhaust system. Since there is a large number of portions that are not leak-tight (hermetically sealed) among the seal portions of the entire system, it is therefore not possible to employ a vacuum evacuation method, even if the atmosphere within the treatment furnace is replaced (purged) with an inert gas, and a method is employed to push out any gases remaining within the treatment furnace by supplying inert gas thereto.
However, in the prior-art oxidation treatment apparatus or oxidation treatment method, it is not possible for an inert gas purge within this method to satisfactorily remove all the factors that will cause the formation of natural oxides, so that when an oxidation treatment is performed by accommodating a semiconductor wafer within a treatment furnace that has been heated beforehand to a predetermined temperature, increasing the temperature within the treatment furnace to a predetermined treatment temperature, and supplying a treatment gas thereto, for example, a problem occurs in that natural oxide films are formed readily in this temperature-increasing step. In addition, as semiconductor devices become even smaller, there is an increasing demand for even thinner oxide films, but the prior-art oxidation treatment apparatus or oxidation treatment method has reached a limit in the formation of superior-quality thin oxide films with uniform film quality and film thickness, due to the occurrence of unwanted natural oxides, which means that the thickness of oxide films obtained thereby has reached a limit on the order of 5 nm.
The present invention was devised in the light of the above described circumstances and has as an object thereof the provision of an oxidation treatment apparatus and oxidation treatment method which are capable of satisfactorily suppressing the formation of natural oxides during a temperature-increasing step, and which are capable of forming an extremely thin oxide film of a superior quality.